0
\$\begingroup\$

block diagram of defibrillator

Please can someone explain the function of L coil in this circuit? This schematic is just medical defibrillator, but almost every capacitor discharge circuit has some series coil.

Is it some kind current limiter?

\$\endgroup\$
5
  • 3
    \$\begingroup\$ It's probably there to shape the pulse and prevent excessive burning due to high inrush current into the patient. \$\endgroup\$ – Andy aka Jun 16 '20 at 11:58
  • \$\begingroup\$ A directly connected defibrilatror? Semms extremly dangourous! L is probably to limit the peak current and/or shape the waveform to something more sinusodial. \$\endgroup\$ – winny Jun 16 '20 at 11:59
  • 1
    \$\begingroup\$ What is the nature of your interest? I hope you aren't building one. \$\endgroup\$ – user16324 Jun 16 '20 at 11:59
  • 1
    \$\begingroup\$ @BrianDrummond Of course, I don't want to build it. My interest is only educational. Because I don´t understand purpose of coil in circuits at all. Except relays and transformers :D :D :D \$\endgroup\$ – Sahasrar Jun 16 '20 at 12:12
  • \$\begingroup\$ @winny It´s not mine. I just copy from Mr. Google :D \$\endgroup\$ – Sahasrar Jun 16 '20 at 12:13
5
\$\begingroup\$

The inductor is there to shape the waveform.

Depending on the values of the capacitor and inductor, the energy from the capacitor will be delivered in a pulse of sine waves around 10 milliseconds long.

The diagram you have is fairly primitive, and dangerous besides - one side of it is still connected to the AC source when defibrillating.

That method of generating and shaping the pulse (as well as the shape of the pulse) also appear to be outdated. The Wikipedia page refers to a newer method (biphasic pulses) that has been in use since the 1980s.

To top it all off, more modern defibrillators use more advanced techniques to generate the pulses so as to deliver enough energy to the heart to stop it (yes, stop it) without causing excessive collateral damage (burns and such.)


The problem that defibrillators "fix" isn't a stopped heart, but a heart whose various muscle sections have gotten out of step.

Rather than beating in step, the muscles are all twitching at various rates. The defibrillator smacks them all and makes them stop.

Thereafter, they start beating again - with a bit of luck, they start up synchronized and stay that way. If not, zap 'em again and hope for the best.

\$\endgroup\$
2
  • 2
    \$\begingroup\$ Nice summary. I can fill in a bit. Cardiac muscle (unlike most other muscles in the body) contracts, and then relaxes. During the relaxation phase, it can not contract again (a period known as "refractoriness"). Other muscles don't have a refractory period. Defib is supposed to contract the whole heart at once, putting all the muscle into a refractory state at the same time, to stop fibrillation. \$\endgroup\$ – Scott Seidman Jun 16 '20 at 13:04
  • 1
    \$\begingroup\$ The monophasic vs biphasic thing is an interesting story that I just started looking into -- as I suspected, the biphasic thing came around with implantable defib, which isn't a surprise -- biphasic is where people automatically go for implantable electrodes, as it discourages irreversable electrochemistry at the electrode/tissue interface. It requires less power transmission (pretty clear), but I'm not sure that's the history of why it came to be. It might be why it spread to external defibs. \$\endgroup\$ – Scott Seidman Jun 16 '20 at 13:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.